powerdns-admin: fix build

[Flakebi]

Description of changes

Fix the build of flask-seasurf and powerdns-admin.
Things got broken by the last flask and werkzeug update.

powerdns-admin.tests succeed with these fixes.

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 23.11 Release Notes (or backporting 23.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

[natsukium]

@ofborg eval

[pbsds]

ZHF #264232, fixes:

• https://hydra.nixos.org/build/238947444
• https://hydra.nixos.org/build/240846908

[Flakebi]

Finally got around to update this PR. Now using patch files instead of search-and-replace (see the two new commits).
I tried again, but it seems like flask-seasurf does not support pytest.

[pbsds]

@ofborg eval

[github-actions]

Successfully created backport PR for release-23.11:

• [Backport release-23.11] powerdns-admin: fix build #271945